Metal species such as metallic ions or elemental metallic residues can cause problems in many industrial chemical processes. For example, metal ions or elemental metallic residues present in a reaction feed may deactivate a catalyst; and metal ions in electronic cleaning solvents may lead the electronic devices to malfunction. In the manufacture of polyester polymers, the presence of metal particles added as catalysts can cause packaging made from these polymers to appear hazy, yellow in color, and often continue to be catalytically active thereby contributing to the formation of acetaldehyde and other color bodies.
Ion-exchange resins are widely used to remove metal ions. Since these resins are made of organic polymers, and are usually used at ambient temperature or slightly above the ambient temperature. Zeolites and activated carbon are widely used as adsorbent for purification or separation. Activated carbon can be used to purify water by absorbing alkaline earth metal ions; zeolite A can remove moisture by acting a desiccant. However, little is known on how to remove metal ions or elemental metallic residues from a system that is highly viscous or from solid solutions at ambient temperature or at slightly higher temperature.
We have discovered that it is desirable to remove metal species in the melt phase reaction for the production of polyester polymers. The continual catalytic effects of some metals have been dealt with by the addition of various catalyst deactivators or thermal stabilizers. Some stabilizers, especially those of the phosphorous acid or esters of various phosphorous compounds are added in quantities which reduce a metal such as antimony to its elemental state, which can contribute to the darkening of the polymer if large amounts of the antimony have to be reduced. It would also be desirable to recover some of these metals as they may no longer significantly contribute to further advantages downstream once their function as polymerization and/or esterification catalysts has concluded.